Address NDK API review feedback

* Add comment on how to use the APIs and the binder call warning
* Change to use size_t for size
* Allow destroy against nullptr
* Add ASystemHealth_getMaxCpuHeadroomTidsSize

Bug: 384944829
Bug: 346604998
Flag: EXEMPT ndk
Test: atest NativeSystemHealthTest
Change-Id: Ia7229e9197a1cd5f1306d2cf672d155ec3899505